The sound of gunshots in the wrong context is a very scary sound. In some contexts, gunshot sounds are not at all out of place, such as in the woods during hunting season or at a firing range. However, in many contexts, both indoors and outdoors, the sound of a gunshot or gunshots is extremely alarming. In many public settings, such as a crowded outdoor marketplace, the sound of gunshots will cause confusion, panic, mob response, and other bad outcomes. However in an indoor environment, the sound of gunshots will often lead to even worse consequences, due to the enclosure of the indoor setting and its associated constrained egress. Getting a quick response from knowledgeable law enforcement officers is critical in minimizing chaos in an indoor gunshot scenario.
Gunshot detection by electronic devices, rather than by humans, is performed for a variety of purposes and applications that include the military, law enforcement, security, and public safety. Gunshot detection is a complex problem because of the variety of weapons and explosive devices that can produce the gunshot event. Identifying the source of the gunshot is critical to identifying and tracking a suspected shooter. The identification of the source of the gunshot is complicated by many factors including the environment in which the gunshot event occurs. Gunshot detection and shooter identification are critical elements in many military, law enforcement, security, and public safety scenarios.
Some early work in detecting gunshots in an outdoor setting involved several microphones spread out over a large distance. A gunshot is often so loud it can be heard many thousands of feet, even miles, away in an outdoor setting. The occurrence of a gunshot would then register on the microphones, but at slightly different times. Because the speed of sound in dry air at sea level at 68° Fahrenheit is about 1125 feet/second, a gunshot somewhere between two microphones that are 2500 feet apart would be detected at the microphones one or even two seconds apart, which is an easily detectable difference. Furthermore, the relative times of detection are an indication of the proximity of the gunshot to one microphone versus another microphone. Unfortunately, this scheme does not distinguish between gunshots and other similar sounds, such as car backfires, construction noises, fireworks, etc.
The difficulty of indoor gunshot detection is many times more complicated than outdoor gunshot detection. For the indoor setting, many complicating factors intrude upon accurate gunshot detection. For example, in an indoor setting, the probability of extensive sound reverberations and echoes from the initial gunshot is very high. In addition, rooms within the indoor setting often have convoluted acoustic pathways. These acoustic pathways are often blocked by closed doors, which cause many decibels of sound attenuation. Furthermore, indoor settings are often spread over multiple floors and replete with crowds of people, which makes handling indoor gunshot situations extremely challenging for law enforcement officers or other public safety personnel. Additionally, many other distracting sonic and visual interferences may be present in a crowded, indoor environment, including screams, flashlights, police alarms, building alarms, fire alarms, earthquake alarms, tornado alarms, and the like. Therefore, accurate gunshot detection in an indoor environment is an important element of public safety that has so far proved to be largely elusive.